GCF for 21 and 87

What is the Greatest Common Factor of 21 and 87?

Answer: GCF of 21 and 87 is 3

(Three)

Finding GCF for 21 and 87 using all factors (divisors) listing

The first method to find GCF for numbers 21 and 87 is to list all factors for both numbers and pick the highest common one:

All factors of 21: 1, 3, 7, 21

All factors of 87: 1, 3, 29, 87

So the Greatest Common Factor for 21 and 87 is 3

Finding GCF for 21 and 87 by Prime Factorization

The second method to find GCF for numbers 21 and 87 is to list all Prime Factors for both numbers and multiply the common ones:

All Prime Factors of 21: 3, 7

All Prime Factors of 87: 3, 29

As we can see there is only one Prime Factor common to both numbers. It is 3

So 3 is the Greatest Common Factor of 21 and 87

Related Calculations

GCF Table

Number 1Number 2GCF
6873
7871
8871
9873
10871
11871
12873
13871
14871
15873
16871
17871
18873
19871
20871
21873
22871
23871
24873
25871
26871
27873
28871
2987
30873
31871
32871
33873
34871
35871

About "Greatest Common Factor" Calculator

This calculator will help you find the greatest common factor (GCF) of two numbers. For example, it can help you find out what is the Greatest Common Factor of 21 and 87? (The answer is: 3). Select the first number (e.g. '21') and the second number (e.g. '87'). After that hit the 'Calculate' button.
Greatest Common Factor (GCF) also known as the Greatest Common Divisor (GCD) or Highest Common Factor (HCF) - it is the largest positive integer that divides each of the integers with zero remainder

FAQ

What is the Greatest Common Factor of 21 and 87?

GCF of 21 and 87 is 3